Implantable devices which monitor and store sensed data and provide alarms when pathological conditions occur will both revolutionize medical care in the near future and also greatly increase our understanding of the physiological and metabolic processes and states that occur in healthy and sick individuals. One obvious area where these devices will have a central role is in the treatment of neurological and cardiac disorders. In the case of cardiac disorders, the ability to monitor, detect, and predict cardiac abnormalities related to, for example, ischemic factors will decrease the fatalities related to these disorders by providing patients with sufficient prior warning to allow them to obtain treatment or intervention prior to having a fatal heart attack.
While coronary narrowing or blockage (e.g., atheroscelerosis, thrombosis, and stenosis) can be treated by angioplasty and the introduction of cardiac stents, subsequent monitoring, after surgical or other type of intervention, would be useful in order to ensure that the effects of an intervention continue to be sufficient. Further, in interventions such as heart replacement, or implantation of a pacing or defibrillation device, follow-up monitoring can provide an ongoing indication that the procedure is having its intended effects. The monitoring system can provide alarm warnings when sensed data indicate that the intervention has become inadequate to deter abnormal cardiac activity. Monitoring of operations of implanted devices (e.g., amount of drug or stimulation delivered over a specified duration), and biological activity which is time-locked to operations of these implanted devices (e.g., post-stimulation activity), and ongoing endogenous biological activity may all be monitored. For example, an increase in the occurrence of responsive therapy, such a pacing therapy, over time may indicate that the heart is getting sicker or that pacing is losing its efficacy.
Fischell et al. in U.S. Pat. No. 6,272,379 discloses an implantable cardiac monitor that can detect ischemia by evaluating the ST segment of a patient's electrogram. Specifically, the ST segment deviation is compared to a threshold, which may be programmed before and/or after the device is implanted within a patient.
Fischell et al. in US Patent Application 2005/0113705 (the '705 application) describes a cardiotracker system which allows for extended recording of cardiac data by transforming the time-series cardiac data into histograms which summarize the cumulative frequency and distribution of various measures of the electrogram. Trending of data and generation of summary results are also described.